This invention relates to a method of characterizing the excitation vector in a processor of speech operative in accordance with code-excited linear prediction (CELP) and, more particularly, to a quantization of a vector representation of speech parameters by employing perceptually important sub-vectors, to be encoded, while other sub-vectors are set to zero. The invention may be referred to as an algebraic vector quantized (VQ) type of CELP speech coder.
CELP speech coding is employed in communication of speech in various types of communication systems, and is particularly useful in cellular or radio telephone systems for compression of voice signals to attain a more efficient use of communication channel space.
The general concept of CELP processing is taught in the following references:
(1) M. S. Schroeder and B. S. Atal, "CODE-EXCITED LINEAR PREDICTION" (CELP); HIGH-QUALITY SPEECH AT VERY LOW BIT RATES; PROCEEDINGS ICASSP (IEEE International Conference on Acoustics, Speech, and Signal Processing), 1985 PA1 (2) J. P. Adoul et al, "FAST CELP CODING BASED ON THE ALGEBRAIC CODE", ICASSP, 1987 PA1 (3) D. Lin, "SPEECH CODING USING EFFICIENT PSEUDO-STOCHASTIC BLOCK CODES; ICASSP, 1987 PA1 (4) ENHANCED VARIABLE RATE CODEC, TR 45.5, PN 3292, 1996 PA1 (5) M. Satoshi et al, "A PITCH SYNCHRONOUS INNOVATION CELP (PSI-CELP) CODER FOR 2-4 KBIT/S ", IEEE, 1994 PA1 (6) C. G. Gerlach et al, "CELP SPEECH CODING WITH ALMOST NO CODEBOOK SEARCH", IEEE, 1994 PA1 (7) R. Salami et al, "8 KBIT/S ACELP CODING OF SPEECH WITH 10 MS SPEECH-FRAME: A CANDIDATE FOR CCITT STANDARDIZATION, IEEE, 1994
Due to the ever increasing use of cellular telephony, there is an increasing need to reduce the amount of communication channel capacity required for transmission of sounds, particularly the transmission of voice signals. There is also a need for high fidelity in the transmission of speech. Presently available equipment does not meet optimally the needs for both high efficiency and high fidelity in the transmission of voice signals.